The invention relates to an electromagnetic pressure valve, having a valve portion for conducting and regulating the pressure of a working medium, such as oil, and having a magnet portion for actuating the valve portion for regulating the pressure of the working medium, in which the magnet portion has a magnet housing with a pole piece, and an adjusting ball is mounted in a hole in the pole piece, and an armature, upon which magnetic force can be exerted as needed, is located in the magnet housing, and a pressure activation threshold to be overcome in the regulation is generated by a spring force of a spring located between the armature and the adjusting ball.
In modern automatic transmissions of motor vehicles that are used preferentially in passenger cars, hydraulically actuated clutches are used to change gears. So that these shifting operations will proceed without bucking and imperceptibly to the driver, it is necessary that the hydraulic pressure be adjusted with maximum pressure precision to predetermined pressure ramps corresponding to the clutches.
For adjusting these pressure ramps, electromagnetically actuated pressure regulating valves are used in the prior art. These pressure regulating valves can be sorted into categories in terms of their construction, namely a seat type or a slide piston type.
One such electromagnetic pressure regulating valve of the seat type is known from German Patent Disclosure DE 19733660 A1.
The use of electromagnetic pressure regulating valves is described for instance in German Patent Disclosure DE 10134115 A1. In it, the hydraulic control is also disclosed in the context of a double clutch transmission.
The pressure level required for actuating the clutches is attained in the prior art by way of a pressure balance integrated with the valve. In this case, a force, which is brought to bear by the electromagnet and is variable as a function of current, is brought into equilibrium with the hydraulic force of the operating medium on the valve seat.
When the principle of a pressure balance is employed, only limited precision of the predefined pressure level is established in actual practice, because of variations in geometry and/or materials. It is therefore necessary to be able to calibrate the value of the pressure at which an equilibrium ensues upon the assembly of the pressure regulating valve. It is therefore standard for so-called adjusting springs to be installed. These adjusting springs must be in contact with an adjusting mechanism, so that the above-described equilibrium of the pressure balance can be shifted to a desired pressure value. This adjustment is effected upon manufacture of the pressure regulating valve, and the valve pressure is measured via a pressure sensor. If the measured actual pressure deviates from the desired set-point pressure, then the initial tension of the compression spring is varied until such time as the desired set-point pressure is established.
Various adjusting mechanisms for the adjusting spring are known from the prior art. Typically, adjusting screws, adjusting bushes, or adjusting caps are used.
From German Patent Disclosure DE 19847304 A1, an electromagnetically actuatable pressure regulating valve is known, in which as an adjusting screw, an adjusting mechanism is shown. From German Patent Disclosure DE 10232293 B4, a further pressure regulating valve is known, in which the spring adjustment, in contrast to DE 19847304 A1, is attained by means of an adjusting bush. The adjusting bush is disclosed there as a slit adjusting bush. An implementation by means of an adjusting cap is disclosed in German Patent Disclosure DE 10255414 A1.
When adjusting screws are used, the initial tension of the adjusting spring is varied in such a way that the adjusting spring, embodied as a compression spring, is braced on the screw, and the spring length is varied by rotating the adjusting screw in accordance with the thread pitch. In pressure regulating valves that are based on the use of adjusting bushes or adjusting caps, however, the spring force is not varied by rotation but rather by an axial displacement of the adjusting components. The adjusting bush or adjusting screw is secured with radial initial tension in a receiving bore, in the manner of a press fit. As a result, the final position, finely calibrated in the final assembly, is maintained when the pressure regulating valve is used.
Since pressure regulating valves in use in automatic transmissions are exposed to severe environmental conditions, securing devices are necessary, to prevent a variation in the pressure to be regulated in operation, or in other words in the range of equilibrium of the pressure balance. In operation of the pressure regulating valve, high oscillatory accelerations occur in particular, which the adjusting mechanism must handle in such a way that no displacement in the spring initial tension results from this oscillatory stress. Thus for this reason, in adjusting screws, a means of securing against relative rotation is employed, using microencapsulated and/or plastic-coated threads. Alternatively or in addition, however, form-locking embodiments are also used. In this case, calked embodiments are an attractive option. In such embodiments, material is positively displaced from an outer part into a screw slot.
While means of securing against relative rotation have proven themselves for adjusting screws, when adjusting bushes or adjusting caps are used only security against displacement with regard to the axial displacement force are necessary. However, then the problem arises that the necessary axial displacement force must not be selected as too high, since otherwise precise adjustment is no longer possible. On the other hand, the force must not be selected as overly low, either, because otherwise unwanted displacement would occur in response to the oscillatory stress. To keep the force within an appropriate range, it is therefore necessary for not only the bushes or cups but also the receiving component to be manufactured with very high precision with regard to the diameter of the cooperating components. From a production standpoint, however, this is very complicated and expensive.
In order to find a solution to this problem, slit adjusting bushes, known for instance from DE 10232293 B4, have been used so far. When such adjusting bushes embodied in slit form are used, markedly less deviation in the adjusting force is found. Because of the slit in the adjusting bush, the interior of the electromagnet that is a part of the pressure regulating valve and is inserted with the outside basically via a bore in which the adjusting bush is located, communicates in unsealed fashion with the environment. As a result, contaminating elements can penetrate into the interior of the pressure regulating valve, and/or an oil filling can be lost from leakage.
To prevent this, a further additional sealing element has so far been installed, such as a sealing ball or plastic cap. This is inconvenient, too, since the assembly takes longer then, and additional parts have to be installed, and since these additional parts have to be kept on hand as well, which in turn leads to an increase in costs.
From the prior art, namely German Patent Disclosure DE 4431459 A1, an electromagnetic pressure regulating valve is also known in which an adjusting ball is located in a bore of a valve cap. The valve cap is located on the side remote from the valve portion of the magnet portion of the pressure valve. Between an armature, into which a tappet is press-fitted, and the adjusting ball, a helical spring is inserted. However, this disclosure has the disadvantage that the helical spring easily buckles, and thus friction occurs between the spring and the valve cap and/or the armature in operation of this pressure regulating valve. That has the attendant disadvantage that the pressure point range of the pressure regulating valve varies, and precise shifting is accordingly no longer possible.